The popularity of microprocessor-based systems and products has resulted in rapid development and production of new equipment to meet the public demand. Such equipment does not lend itself to diagnosis of faults or malfunctions by conventional testing and trouble-shooting instruments, such as oscilloscopes and the like, because information provided by these instruments is limited or incomplete, and subject to interpretation. Efforts to develop new diagnostic test equipment to service microprocessor-based systems has resulted in such techniques as self-diagnosis by following a predetermined checkout procedure, in-circuit emulation in which an external device emulates or imitates the functions of a host microprocessor, and signature analysis by probing for correct signatures at predetermined test points. While such diagnostic techniques are a step forward, they fail to provide a complete diagnostic capability. For example, self diagnostics are useless in situations where the kernel of the product is down, and prior external devices are typically complex and require considerable skill in operation, and do not give a complete diagnostic capability of both analog and digital measurements.